The invention relates to an apparatus for controlling the power drive of a vehicle, having a mechanical transmission device interposed between the actuator determining the drive power output, such as a throttle valve, and the drive power operating element, such as the accelerator pedal; in this transmission device, an adjusting element that has a stop and is movable by a regulating device to adjust the actuator is movable, counter to the action of one or more springs and relative to a coupler of the transmission device that has a counterpart stop, from an unregulated position, in which stops rest on one another, to regulated positions, in which stops are spaced apart from one another.
Such an apparatus is known, for instance from German Offenlegungsschrift 36 08 751.
Regulating devices coupled to the mechanical transmission device are used in order to provide the actuator with a position deviating from its position predetermined by the operating element, for instance to avoid drive slip, or to provide progressive pedal characteristic curves, or to vary shifting processes in automatic transmissions. The adjusting element moved by the regulating device is held in a regulated position in this process, counter to the action of the springs, from which position it is moved by the springs suddenly into its unregulated position, if the regulating device fails, for instance if the electrical system fails; this can lead to reactions by the vehicle that are entirely unexpected and cannot be foreseen by the driver. If the regulating device fails during a mode in which the speed is being kept constant, the actuator returns astonishly suddenly into its idling position, which is equivalent to an abrupt let up on the gas. If the regulating device fails while the driver is calling for half acceleration with the operating element and the regulating device, because of a progressive pedal characteristic curve, keeps the actuator nearly at idling, then the vehicle accelerates astonishingly suddenly in a way that profoundly surprises the driver.